The present invention generally relates to methods and apparatuses for adding slurry to a semiconductor wafer polishing system, and more specifically relates to a method for adding slurry in a semiconductor wafer polishing system by adding the slurry through a wear ring. The present invention also specifically relates to a wear ring which is configured to facilitate the adding of a slurry therethrough, in a semiconductor wafer polishing system.
An IC chip is a sandwiched, multiple layer structure which typically includes a silicon substrate, dielectric layers, metal interconnects, devices and so on. Every layer is formed by deposition, photolithographic, etching, as well as other, techniques. Every layer must be planar and, as the features get smaller, the requirement for planarity gets more stringent. Chemical Mechanical Polishing (CMP) plays an important part in planarizing every layer before the next top layer is deposited. The CMP process involves pressing the face of the wafer to be polished against a compliant polymeric polishing pad and generating relative motion between the interface between the wafer and the pad. A slurry consisting of abrasives and chemicals is fed in between the interface between the wafer and the pad. The combined chemical action of the chemicals in the slurry and the mechanical action of the abrasives cause material to be removed from the wafer. A typical CMP setup looks very similar to a lapping machine, but the precision is much higher and there is a lot more sophistication.
One of the most commonly-used devices for polishing a semiconductor wafer is a rotational format CMP machine as illustrated in FIG. 1. The wafer 10 is held in a wafer carrier by a wear ring 12, and is pressed against a polishing pad 14 which is disposed on a polishing table 16. Both the wafer ring 12 and polishing table 16 are then rotated (as indicated by arrows 18 in FIG. 1), and slurry is supplied on the pad 14.
Presently, there are two widely-used ways of adding slurry to a semiconductor wafer polishing system. A first method provides that slurry is added through the polishing pad 14. A second method provides that slurry is dripped on the polishing pad 14, proximate the wear ring 12. The method wherein slurry is added through the pad is generally regarded as being the preferred method because only about half as much slurry is used. This is a major cost savings as slurry is costing up to $4.00 per step, with ten or more steps being performed per wafer. In addition to providing a cost savings as a result of less slurry being used, the method wherein slurry is added through the pad also provides that the full wafer surface is wetted with slurry at the same time, and this is advantageous.
A wear ring (indicated with reference numeral 12 in FIG. 1) is a ceramic ring which holds the wafer 10 during the polishing process. Generally, the wear ring is a major barrier to the slurry getting to the wafer. As the wafer moves on the polishing table, the wear ring pushes much, if not most, of the slurry away from the wafer. The bigger the wafer, the bigger the problem this presents.
Generally, two methods have been widely-used with regard to attempting to improve getting the slurry across the wear ring and under the wafer. In one method, grooves are provided in the polishing pad, both in the x and y directions and concentric. In the other method, grooves are not only provided in the polishing pad, but also in the wear ring. Regardless of which method is employed, too much slurry must be used, and the problem persists of the slurry not getting to the wafer due to the wear ring blocking the slurry.